1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to operation of an apparatus of an electrophotographic system that develops an electrostatic latent image formed on an image bearing member with a developer, and transfers and fixes a developed toner image onto a recording medium to perform image formation.
2. Description of the Related Art
An image forming apparatus such as a laser printer includes a video controller (controller part) that receives print information from a host computer, performs analysis of the information and image processing, and generates video data for printing. Further, there is provided an engine (engine control part) communicatably connected to the video controller to perform image forming operation according to the video data from the video controller. Among apparatuses of this type, there are apparatuses configured to combine the video controller and the engine together, which are different in function from each other.
The video controller and the engine are configured to be communicatable with each other so that the video controller transmits, to the engine, various instructions related to image formation as commands, and the engine returns, to the video controller, an internal state of the engine as a status.
When the print information is transmitted from the host computer to the video controller, the video controller analyzes the print information, and transmits a reservation command of the printing operation to the engine. Upon completion of image processing, the video controller transmits a print starting command for reserved printing operation to the engine. Upon receiving the print starting command from the video controller, the engine shifts the state of the engine from a standby state to a print state enabling printing operation, and starts printing operation. After the printing operation starts, that is, in shifting from the standby state to the print state, various actuators such as a motor which is a drive source for conveying a recording medium start up. Further, various units for charging, exposure, development, transfer, and fixing required for an electrophotographic process start up together. It is necessary that the startup of those units is executed at a predetermined timing and in a predetermined order. The startup is a pre-processing step conducted before printing operation, and the pre-processing is called “pre-rotation”.
When printing operation is executed in the print state, and there is no reservation command to be processed which is issued from the video controller, it is determined that all of the printing operation has been completed, and the various actuators and the various units stop so as to again shift to the standby state. This operation is a post-processing step conducted after the printing operation, and the post-processing step is called “post-rotation”.
A period of time required for the pre-rotation and the post-rotation is different depending on the size of the laser printer, or the operating speed thereof, and ranges from around several seconds to around several tens.
For that reason, there arises the following problem. The engine determines that there is no reservation of print to be processed and the printing operation has been completed at the time of the print state, and then starts post-rotation. When a new print reservation command (reservation of printing operation) and a print starting command (start of printing operation) are transmitted from the video controller to the engine immediately after the post-rotation starts, there arises the following problem.
With the conventional technology, once the engine starts the post-rotation, the engine cannot stop the post-rotation on the way, and executes the post-rotation to the last. Since the engine is in a standby state at the time of completing the post-rotation, the printing operation cannot start unless the engine executes the pre-rotation from that state and enters the print state in order to follow an instruction from the video controller.
That is, the printing operation has to wait while both the post-rotation and the pre-rotation are executed, in which a new print starting command is received from the video controller, the engine enters a printable state, and the printing operation actually starts. The wait time is called “down time”.
On the other hand, a timing at which the engine starts the post-rotation is called “print continuation timing”. When the video controller transmits the print reservation command to the engine before the print continuation timing, the engine does not start the post-rotation.
The above-mentioned problem arises, for example, when the reservation of the printing operation from the video controller is not notified by a timing necessary for continuing the contiguous printing operation, that is, when a subsequent print reservation command is transmitted from the video controller with a delay.
In order to solve occurrence of the down time, there have been proposed a variety of systems. For example, there has been proposed a system in which a command for notifying a delay of the print reservation command is prepared so that the engine is prevented from entering the post-rotation even if the video controller cannot transmit the print reservation command for a subsequent page by the print continuation timing. When the engine receives the command (print reservation delay command) from the video controller, a timing when the engine enters the post-rotation is extended (for example, refer to Japanese Patent Application Laid-Open No. 2006-015515).
However, if the timing when the engine enters the post-rotation is extended, the engine continues the print state. Some units of the engine consume their lifetimes just because they are in the print state. For example, those units include components of a process cartridge (consumable) that is detachably attached to the laser printer. Hereinafter, the process cartridge is described in brief.
The process cartridge has been widespread as a unit detachably attached to the laser printer for the main purpose of recycling a resource. The process cartridge of this type integrally includes a photosensitive drum, a charger, an exposing unit, a developing unit, a cleaner, and a toner container necessary for image formation in the electrophotographic process system. Among the respective components of the process cartridge, for example, the photosensitive drum and a developing roller of the developing unit each have a lifetime. When a rotation time of the photosensitive drum or the developing roller is counted up, and the counted accumulative value reaches a given threshold value, it is determined that the lifetime of the process cartridge is ended, and a user is urged to replace the process cartridge.
If the timing when the engine enters the post-rotation is extended, no down time occurs. However, there arises such a problem that since the components of the process cartridge, such as the photosensitive drum and the developing unit, still operates, those components are fast consumed (an increase in rotation time of the photosensitive drum and the rotation time of the developing roller).
It has been difficult to solve, at the same time, both of the two problems, by which the down time is reduced, and the lifetime of the consumables of the process cartridge is prevented from reducing.